A study by researchers at Iowa State University has found that hybrid-electric school buses burn significantly less fuel than comparable diesel buses. However, the hybrid vehicles have been plagued by charging problems that prevented the buses' electric motors from working.
The study looked at how two plug-in hybrid electric buses performed — one used by the Nevada (Iowa) district, and the other used by the Sigourney (Iowa) district. The Nevada bus achieved fuel economy 30 percent better than a comparison diesel bus, and the Sigourney bus achieved fuel economy that was 36 percent higher than a comparison bus.
But problems with the charging systems prevented the batteries from taking a charge. That prevented the buses' electric motors from working, and the V-8 diesel engines had to power the buses instead. The charging problems occurred more frequently in cold weather, the school districts reported.
Other hurdles that the hybrid buses must overcome, the researchers say, include developing a battery system that sustains a charge over longer routes; heating the bus interior when the electric motor rather than the heat-producing diesel is used in the winter; and reducing tire wear caused by the extra weight of the hybrid system.
